1. Field of the Invention
The present invention relates to a dielectric ceramic, a method of manufacturing a dielectric ceramic, and multilayer ceramic capacitor (MLCC) constituted by dielectric ceramics stacked densely.
2. Description of the Related Art
As mobile phones and other digital electronic devices become increasingly smaller and thinner, laminated ceramic electronic components that are surface-mounted on electronic circuit boards, etc., are getting smaller. In particular, multilayer ceramic capacitors that are laminated ceramic electronic components are seeing growing requirements every year for capacity increase to support decreasing chip sizes. Multilayer ceramic capacitors have a structure whereby dielectric layers constituted by dielectric ceramics and internal electrode layers are stacked alternately.
In general, reducing the capacitor size inevitably reduces the area of the electrode layers facing the dielectric layers and therefore decreases the capacitance. Accordingly, it is essential, in ensuring enough capacitance of the capacitor to support decreasing chip sizes, to make the dielectric layers and electrode layers thinner and incorporate technology to densely stack them in multiple layers.
In the meantime, among the known dielectric ceramics offering good dielectric constant vs. temperature characteristics are those whose ceramic crystal has a core-shell structure. For example, it is known that, by adding to the primary component of BaTiO3 (barium titanate) a component that contains rare earth metal, etc., and then sintering the component mixture while suppressing grain growth, dielectric ceramics of core-shell structure whose dielectric constant is subject to minimal temperature-dependent change can be obtained (refer to Patent Literature 1, for example).
According to Patent Literature 1, ABO3 compound (A represents Ba, Ba—Ca or Ba—Ca—Sr, while B represents Ti or Ti—Zr) is used as the dielectric ceramic component, where the average grain size of the material powder thereof is 0.1 μm to 0.3 μm. The requirements for obtaining the specified temperature characteristics include the sintered ceramic crystal meeting “Core size<0.4×Grain size” and the average grain size being in a range of 0.15 μm to 0.8 μm.